This invention relates to hydraulic presses and more particularly to high-speed hydraulic presses.
The most simple hydraulic presses are those wherein both the approach of the working ram to the work piece, as well as its working motion are effected by systems supplying pressurized hydraulic medium to the hydraulic cylinder of the press. As a result, an approximately constant rate of travel of the ram and, consequently, a uniform pressure over the entire length of the stroke of the ram are obtained. The disadvantages of this system are that considerable power losses are caused by the existence of a large pressure force existing during the idle run of the ram, that is during the approach of the ram of the work piece and, at the same time, smaller speed of the system caused by a limited delivery of the hydraulic pump in the hydraulic supply circuit.
In another known hydraulic press, these disadvantages are eliminated by providing an additional hydraulic system for a rapid piston traverse in the initial stage of the motion corresponding to the approach of the ram, and, providing two hydraulic systems for feeding the main pressure chamber, namely, a suction system operating in the first stage of the motion corresponding to the approach movement of the ram and a system for `supercharging` the chamber with a pressurized hydraulic medium in the working stage of the piston traverse. In a press having such hydraulic systems the speed of the ram approach motion is increased, the pressure force of this motion is reduced, and the pressure force of the working motion is increased. However, serious drawback of this press is aeration of its main pressure chamber observed in a case when the ram approach motion has been too rapid, which in practice restricts the speed of the press. Moreover, presses of this kind have complicated hydraulic systems with sophisticated controls, and many valves of which the suction valves with large flow rates have relatively long resetting times and thus restrict the speed of the press.
In another known press, the above mentioned drawbacks have been eliminated by providing two independent hydraulic systems for feeding the main pressure chamber, namely, a system with a high delivery and low pressure for feeding the chamber during the approach motion, as well as a high-pressure system for the working motion of the ram. Hydraulic presses of this kind can have considerably higher speeds than the above mentioned press. On the other hand, the above mentioned press has also some drawbacks, namely, it must have two independent hydraulic systems and a relatively sophisticated control system, the speed of the press being limited by the necessary time for resetting the system from one working mode to another.